New Theme object, to manage theme configuration.
Reads in themeconfig.php for all themes. Allows the theme objects to set their own fields if necessary. The root theme is now 'raw', and this cannot be changed. All themes extend from the raw theme. A bunch of fields were added to do with the widths and colours of the columns. Now, it's technically possible for a Mahara site to have sideblocks on the left, or sideblocks on both sides, and the widths of these columns can be set in pixels or percent.